• ** REMEMBER! **The microwave can still shock you even unplugged!!

    ALWAYS discharge the high-voltage capacitor first if you even think your hands will come close to any HIGH VOLTAGE components.

    Jeff mentions this: Anything in the high voltage ( magnetron, capacitor, diode, wires to and from ):
    ...Use a metal ( not the shiny chrome type ) screw driver with a insulated handle to short across ( touch both at the same time ) the terminals of the high voltage capacitor to discharge it.

    From Jeff's site: http://www.applianceaid.com/component-testing.php

    Jake

FIXED 566.8832980 Microwave Comes On And Hums But No Heat

jimmy12345678

Premium Member
Joined
Jun 27, 2017
Messages
3
Location
WV
Model Number
566.8832980
Brand
Sears Kenmore
Age
More than 10 years
The other day I went to heat up food in my Kenmore microwave and after about 15-20 seconds there was smoke rolling out of it. So I unplugged it and took the cover over to see what was wrong. I ran it with the cover off and noticed that the transformer was getting very hot and that's what was smoking, so I found another one that would fit and installed it. Now the microwave turns on and doesn't smoke, but it also doesn't make things hot. I put a cup of water in there for a minute and it was still ice cold.

I've searched online and found Microtech Factory Service and they had diagnostic procedures to test the various components inside a microwave. I'll post the results of those tests below:

Transformer

Between Primary Windings - 0.2 ohms (Old and New)
Between Primary Leads And Ground - Open
Between Filiment Wires - 0.2 ohms (Old and New)
Between Filiment Leads And Ground - Open (Old and New)
Between Voltage Tap and ground - Old One - 848 ohms (spec says 55-70 Ohms) New One - 102 Ohms I don't know if this is too far out of spec or not

Magnetron:

Between Both Terminals - 0.2 Ohms
Between Terminals And Ground - Open

Capacitor:

Between both terminals - Slowly climbs to OL, when switched goes back to zero and starts climbing back to OL
Between terminals and ground - Open

Diode:
0.2M Ohms one way
OL other way


Thermal Protectors (2)

Both 0.2 ohms across terminals


It just doesn't make any sense why it doesn't work now. It worked on Saturday, then yesterday I used it and that's when the transformer overheated. And I didn't touch anything else inside, just wired up the new transformer just as the old one was. Same specs on both of them (120v, 60 Hz). Unless this new transformer is also defective (as I said, the 102 Ohms on the voltage is above the spec I found).

If anyone can help me or they need me to conduct more tests I'm more than happy to help. Thanks!!! I can't stand to see this microwave die.
 
Last edited:

jeff1

Appliance Tech - Moderator
Staff member
Joined
Oct 10, 2004
Messages
23,700
Location
Ontario, Canada
Hi,

A copy:

Q - Hello, My Microwave Oven is about 5 years old and won't heat food anymore. Any hints on what electrical circuits to check?

A - Confirm 110-120 volts AC is entering the primary coil on the high voltage transformer....meter works but can be fooled, I usually rig up a light socket and household light bulb and hook that to the 2 input wires for the transformer and see if the light works or not when you run the microwave....can even set a power level and watch the light go on and off. Discharge the capacitor first before attempting any checks or tests.

Scary but works!....

If ok, put those 2 wires back on the transformer. Discharge the capacitor.

Remove the 2 wires going to the magnetron....run the microwave a few seconds ( 2-3 ) and remove power....again discharge the high voltage capacitor. If you got a good crack & spark when you discharge the cap the second time you are creating high voltage but not using it ( bad magnetron or loose High Voltage wire somewhere )....if you get no crack & spark you are not creating high voltage. This will work on all microwaves with a transformer and diode system ( not the inverter style ).

jeff.
 

jimmy12345678

Premium Member
Joined
Jun 27, 2017
Messages
3
Location
WV
I made a test light out of an old lamp socket and hooked it up to the primary leads on the transformer and it lit up when set on high power. I tried various power settings and the light would kick on and off at various times depending on the setting.

I then unhooked the wires going to the magnetron and ran the microwave on high power for 3 seconds. Then I discharged the capacitor and it made a big crack and spark, which means everything on the high voltage side up to the magnetron is good. So I've ordered a replacement magnetron on ebay and am waiting for it to show up.

Thank you so much for helping me diagnose this!!! I'll update this thread once the part gets here and I get it installed.
 

jimmy12345678

Premium Member
Joined
Jun 27, 2017
Messages
3
Location
WV
My new magnetron arrived in the mail today, so I tore the old one off and transferred the mounting bracket and air ducts mounted on it to the new one. Then I installed the new one and tested everything and it's working as it should again. I tested it with a cup of water and after 1 minute the water was pretty warm, not ice cold as before. This repair has been a total success, and I've learned how to repair microwaves in the process. Thanks so much to everyone who helped me along the way!!!
 

jeff1

Appliance Tech - Moderator
Staff member
Joined
Oct 10, 2004
Messages
23,700
Location
Ontario, Canada
Thankx for the update.

jeff.
 
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